Solved: C# Socket blocking problem

All, I have been trying to cobble together a working version of a program that receives messages from a host and send a response back. There is an example message in one of the methods. Line 197's intent is to send a response back to the sender notifying the sender that I have accepted their message (without this response their system will keep trying to send and resend the message)

I have been getting a blocking error from the senders side, and this :

Unable to read data from the transport connection: A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond. (also from the senders side)

Can someone steer me in the right direction as to what I am doing wrong or how to fix this?

Here is the code:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Threading;
using System.Net.Sockets;
using System.Net;

namespace HL7ReceiverTest
{
public partial class Form1 : Form
{
List<String> TestMsg;
public Form1()
{
InitializeComponent();
SetTestVariables();
}

private void SetTestVariables()
{
TestMsg = new List<String>();
TestMsg.Add(@"MSH|^~\&|Some dumb RIS|Some dumb location|Some Dumb PACS||20200402144906||ORM^O01|2004021449067041|P|2.3.1");
TestMsg.Add(@"PID | 1 | 189.60787 | 280384 | 999 - 99 - 9999 | OGRE ^ FIONA ^ HAGATHA || 19740119 | F ||| PO BOX 001 ^ STE 233 ^ City ^ State ^ 12345 ^ US || (501)555 - 1212 ^^ (501)555 - 9876 | (501)581 - 3493 ||||| 999 - 99 - 9999");
}

static private List<String> CreateAck(List <String> DataList)
{
List<String> Results = new List<string>();
foreach (String St in DataList)
{
if (St.Contains("MSH"))
{
String[] DBts = St.Split('|');
Results.Add(DBts[0] + "|" + DBts[1] + "|" + DBts[4] + "||" + DBts[2] + "|" + DBts[3] + "|" + DBts[6] + "||ACK^O01|" + DBts[9] + "|" + DBts[10] + "|" + DBts[11]);
Results.Add("MSA|AA|" + DBts[9]);
}
}
return (Results);
}
static private List<String> CreateAck(String Data)
{
List<String> Results = new List<string>();
int Pt0 = -1;
int Pt1 = -1;
Pt0 = Data.IndexOf("PID|");
Pt1 = Data.IndexOf("MSH|");
if(Pt0>Pt1 && Pt1>=0)
{
String TData = Data.Substring(Pt1, Pt0);
String[] DBts = TData.Split('|');
Results.Add(DBts[0] + "|" + DBts[1] + "|" + DBts[4] + "||" + DBts[2] + "|" + DBts[3] + "|" + DBts[6] + "||ACK^O01|" + DBts[9] + "|" + DBts[10] + "|" + DBts[11]);
Results.Add("MSA|AA|" + DBts[9]);
}

return (Results);
}

static private int GetDateKey()
{
int Results = -1;
String TmpResult = DateTime.Now.ToString("yyyyMMdd");
Results = Convert.ToInt32(TmpResult);
return (Results);
}

private int GetDateKey(DateTime Data)
{
int Results = -1;
String TmpResult = Data.ToString("YYYYMMDD");
Results = Convert.ToInt32(TmpResult);
return (Results);
}

private void button1_Click(object sender, EventArgs e)
{
StartListening();
}

private void button2_Click(object sender, EventArgs e)
{
Application.Exit();
}

public class StateObject
{
// Client socket.
public Socket workSocket = null;
// Size of receive buffer.
public const int BufferSize = 4098;
// Receive buffer.
public byte[] buffer = new byte[BufferSize];
// Received data string.
public StringBuilder sb = new StringBuilder();
}

public static ManualResetEvent allDone = new ManualResetEvent(false);

public static void StartListening()
{
// Establish the local endpoint for the socket.
// The DNS name of the computer
// running the listener is "host.contoso.com".
IPHostEntry ipHostInfo = Dns.GetHostEntry(Dns.GetHostName());
IPAddress ipAddress = ipHostInfo.AddressList[3];
IPEndPoint localEndPoint = new IPEndPoint(ipAddress, 11000);

// Create a TCP/IP socket.
Socket listener = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);

// Bind the socket to the local endpoint and listen for incoming connections.
try
{
listener.Bind(localEndPoint);
listener.Listen(100);

while (true)
{
// Set the event to nonsignaled state.
allDone.Reset();

// Start an asynchronous socket to listen for connections.
Console.WriteLine("Waiting for a connection...");
listener.BeginAccept(
new AsyncCallback(AcceptCallback),
listener);

// Wait until a connection is made before continuing.
allDone.WaitOne();
}

}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
Console.WriteLine("\nPress ENTER to continue...");
Console.Read();

}

public static void AcceptCallback(IAsyncResult ar)
{
// Signal the main thread to continue.
allDone.Set();

// Get the socket that handles the client request.
Socket listener = (Socket)ar.AsyncState;
Socket handler = listener.EndAccept(ar);

// Create the state object.
StateObject state = new StateObject();
state.workSocket = handler;
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);
}

public static void ReadCallback(IAsyncResult ar)
{
List<String> Notes = new List<string>();
String content = String.Empty;

// Retrieve the state object and the handler socket
// from the asynchronous state object.
StateObject state = (StateObject)ar.AsyncState;
Socket handler = state.workSocket;
EndPoint EP = handler.RemoteEndPoint;
String IPA = EP.ToString();
String ClientAddress = IPA.Substring(0, IPA.IndexOf(':') );
// Read data from the client socket.
int bytesRead = handler.EndReceive(ar);

if (bytesRead > 0)
{
// There might be more data, so store the data received so far.
state.sb.Append(Encoding.ASCII.GetString(state.buffer, 0, bytesRead));
content = state.sb.ToString();
Notes.Add(content);
handler.BeginReceive(state.buffer, 0, StateObject.BufferSize, 0,
new AsyncCallback(ReadCallback), state);
}
if(bytesRead==0)
{
String HL7Response = "";
String TData = state.sb.ToString();
List <String> HL7Lines = CreateAck(TData);
int DKey = GetDateKey();
foreach(String Line in HL7Lines)
{
HL7Response += Line;
}
Send(handler, HL7Response);
}

}

private static void Send(Socket handler, String data)
{
// Convert the string data to byte data using ASCII encoding.
byte[] byteData = Encoding.ASCII.GetBytes(data);

// Begin sending the data to the remote device.
handler.BeginSend(byteData, 0, byteData.Length, 0,
new AsyncCallback(SendCallback), handler);
}

private static void SendCallback(IAsyncResult ar)
{
try
{
// Retrieve the socket from the state object.
Socket handler = (Socket)ar.AsyncState;

// Complete sending the data to the remote device.
int bytesSent = handler.EndSend(ar);
Console.WriteLine("Sent {0} bytes to client.", bytesSent);

handler.Shutdown(SocketShutdown.Both);
handler.Close();

}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
}

private void Document(String SenderIP, String HL7)
{

}
}
}